Device for protection of the anode of power electron beam gun

ABSTRACT

A method and apparatus for minimizing electron impingement of an anode in an electron beam gun by measuring the operating temperature of the anode and automatically adjusting the focusing electrode potential as a function of the anode temperature to reduce electron impingement of the anode.

- United States Patent 3,418,520 12/1968 Barberetal.................. FrlederlEmlimbothoiR 3,471,640 10/1969 Tanner 854,548

[72] Inventors Robert QM OTHER REFERENCES 211 App]. No. 221 Filed Sept-2.1 e Barber & Collins 45 Patented Alla- Size Control v01. 10, No.2, 7/67.

Beam Spot IBM Technical Disclosur 13] Assignee maniacalin ODE OF [54] DEVICE FOR PROTECTION OF THE AN POWER ELECTRON BEAM GUN 9 Chile, 2 Drawing Figs.

[52] US. Cl

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315/31 ABSTRACT: A method and apparatus for minimizin 31 TV, 30, 3]

[51] Int." [50] tron impingement of an anode in an electron beam gun by measuring the operating temperature of the anode and auto- [56] R cm matically adjusting the focusing electrode potential as a func- UNITED STATES PATENTS tion of the anode temperature to reduce electron impingement of the anode.

TO CATHODE POWER SUPPLY POWER 8U PPLY TO SIGNAL AMPLIFIER DEVICE FOR PROTECTION OF THE ANODE OF POWER ELECTRON BEAM GUN BACKGROUND This invention relates to electron guns, electron beam discharge devices, and more specifically, to the control of the electron beam within the gun. I

Electron guns, to be efficient, must generate concentrated,

high current density electron beams of small cross section. To

accomplish this the electrons are accelerated and focused within a tube which containsapertured electrodes (focusing, accelerating, etc.) which permit the passage of the electron beam. Examples of electron guns having apertured electrodes may be found in U.S. Pat. Nos. 2,986,672; 3,185,882; and 3,139,552. A common problem associated with power electron beam guns is thermal overloading (overheating) of the accelerating electrode or electrodes as a result of electron bombardment which in certain cases can result in melting of the electrode and/or the surrounding structure. The impinging of electrons on the accelerating electrode (e.g. anode) is undesirable as this decreases the efficiency of the electron gun and causes the temperature of the anode to rise so that in some instances cooling means.(e.g. coils for'circulating a coolant) are required to keep the anode operating temperature at a reasonable level. Generally, the cooling means are bulky and expensive to build and operate. Further, over cooling cancause condensation of, moisture onto the electron beam gun which is very undesirable in the presence of high operating potentials. Also associated with the problem ofthermal overloading is the problem of selecting an accelerating electrode (c.g. anode) having the correct size aperture to pass mostof the electrons from the cathode to a target so that the electrode will not be thermally overloadedv by impinging electrons. Another problem related to the operation of an electron beam gun in a sputtering apparatus is the transfer of maximum power from the cathode of the electron gun to the target to be sputtered.

SUMMARY OF THE INVENTION To eliminate thermal overloading of the anode (accelerating electrode) resulting from electron bombardment and to increase the operating efficiency-of an electron beam gun the focusing electrode whichis mounted between the cathode and the anode, has a controllable negative potential applied to it which varies as a function of the temperature of the anode. The temperature of the anode is sensed by a thermocouple located as close aspossible to the anode aperture and anegative potential is applied to theifocusing electrode in response to changes in the anode temperature so that when the temperature of the anode increases, the negative potential on the focusing electrode increases. This decreases the electron beam current, causes a reduction in electron bombardment of the anode, and lowers the anodes operating temperature. The invention is characterized by an electron gun having .means to sense the temperature of the accelerating electrode and control the negative potential applied to the focusing electrode in response to variations in temperature.

Accordingly, it is an object of this-invention to minimize the electron bombardment of an accelerating electrode in an electron beam gun. g

It is another object of this invention to retard the thermal overloading of accelerating electrodes by impinging electrons in an electron gun by controlling the negative potential applied to the focusing electrode as a function of thetemperature of the anode.

It is a further object of this invention tov increase the operating efficiency of an electron beam gun.

It is a further object of this invention to obtain a maximum transfer of power from the cathode to the electron beam tar get.

It is still another object of this invention to eliminate the necessity for cooling the anode in an electron beam gun.

It is yet another object of this invention to optimize the size of the anode aperture in an electron beam gun.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification.

BRIEF DESCRIPTION OF DRAWINGS F IG. 1 is a block diagram of the invention. FIG. 2 is a partial diagrammatic view of an electron beam gun showing the location of the temperature sensing device.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 shows a block diagram of a system for changing the negative potential applied to the focusing electrode (control electrode) of an electron beam gun in response to changes in the temperature of the anode. The temperature sensor, which can be, but is not limited to a thermocouple, a plurality of thermocouples, or a thermister has the sensor connected to the anode of the electron gun and the sensor output connected to a signal amplifier. The signal from the amplifier is transmitted to a control power supply, which has its negative lead connected to the focusing electrode of the electron beam gun. The output of the temperature sensor is shown connected to a readout device for visual indication of the anode temperature. Shown in dotted lines is the target which is subject to bombardment by the electrons of the electron beam gun.

FIG. 2 is a partial diagrammatic view of an electron beam gun 10 showing the electrical connections of the temperature sensor (thermocouple junction 21) to the anode 11. The electron gun 10 utilizes a filamentary cathode 18, although other types of cathodes may be used to generate electrons. The cathode filament 18, although other types of cathodes may be used to generate electrons. The cathode filament 18 is energized by a filament power supply (not shown) and when heated emits electrons. The focusing electrode 12 and anode 11 form and accelerate these electrons into an electron beam 1. An anode 11, having an aperture 13 (preferably round) to permit the passage of electron beam 1 is disposed downstream of the cathode 18. The electron beam 1, after emerging from the anode aperture 13, continues through tube 15 where it strikes target 50. To sense the temperature of the anode 11, thermocouple 21 is attached as close as possible to the anode aperture 13. Electrical conductors 22, 23 transmit the signal developed by thermocouple 21 through the temperature signal amplifier to the control power supply (FIG. 1). A preferred thermocouple would be to have one of the electrical conductors, e.g. 23, composed of a metal dissimilar to the metal of the anode 11. Then dissimilar metal conductor, i.e. 23, when welded to the anode forms the thermocouple junction 21. The thermocouple may be chosen for its heat resistance characteristics from any standard catalog (e.g.) Reference Data for Radio Engineers, International Telephone and Telegraph, 4th Edition). The preferred thermocouple is copper constantan, formed by the copper anode 11 which is the extension of copper wire lead 22 and a constantan wire lead 23 which is welded directly to the anode. Welding of the constantan to the copper anode assures good thermal contact and prevents contamination of thethermocouple by a foreign material. Also, only the constantan wire need be welded close to the anode aperture. The copper wire which forms the other lead from the thermocouple, can be disposed at any convenient location on the anode. The control power supply (FIG. 1) receives the temperature signal and applies a nega- OPERATION Referring now to the drawings, the invention protects the anode from electron bombardment as follows: When the elec-' tron gun is operating, electrons emitted by the cathode 18 are formed into an electron beam 1 by potentials applied to the anode l l and the focusing electrode 12. The potential applied to the anode accelerates the electrons from the cathode 18 to the anode 11. The negative potential applied to the focusing electrode 12, from the control power supply, electrostatically focuses the electron beam 1 so that it passes through the anode aperture 13 and strikes target 50. The electron beam 1 may also be magnetically focused by a magnetic focusing coil (not shown) so that it strikes target 50 as a dense electron beam. If the focusing electrode 12 is not biased properly, all the electrons emitted from the cathode 18 may not pass through the anode aperture 13, but instead may strike the anode l l causing thermal overload of the anode 1 1 which can result in melting. To prevent damage of the anode (evaporation or thermal deformation to the anode and/or the surrounding structure), thermocouple 21 senses the temperature of the anode 11 and transmits a signal through the temperature amplifier (FIG. 1) to the control power supply which changes the negative potential on the focusing electrode 12 in response to variations in the temperature of the anode.'For example, when the temperature of the anode 11 increases, the magnitude of the focusing electrode potential is increased until the anode temperature returns to an acceptable operating value. An acceptable (safe) operating temperature is one which does not adversely effect the electron gun operation or structure.

The device was also used to select the optimum size of an anode aperture 13 as follows: An electron beam gun 10, which permitted removal and replacement of the anode 11 from a fixed position, was energized and the potential on the focusing electrode 12 was maintained at a fixed value. Then, the current flowing to the target 17, as a result of electron beam 1, was measured along with the anode temperature. This operation was repeated for anodes having different size apertures. Then the anode having the proper aperture size was selected by choosing the anode 11 having the highest acceptable operating temperature while yielding a given electron current flowing to the target 50. The acceptable operating temperature being based upon the highest temperature which any of the electron beam gun components could be subjected to without any adverse effects.

While I have disclosed a preferred embodiment of my invention, it will be apparent to those skilled in the art that changes may be made to the invention as set forth in the appended claims and, in some cases, certain features of the invention may be used to advantage without corresponding use of other features. For example, in an electron gun having a plurality of apertured electrodes, the temperature of any one of the electrodes may be used to control the potential applied to another electrode and in some cases the power supplied to the cathode may be controlled as a function of the temperature of one of the electrodes. Accordingly, it is intended that the illustrative and descriptive materials employed herein be used to illustrate the principles of the invention and not to limit the scope thereof.

Having described the invention, 1 claim:

1. In combination with an electron gun having an accelerating electrode and a focusing electrode, the improvement comprising:

means for sensing the temperature of said accelerating electrode; and

means for applying a negative potential to said focusing electrode of said electron gun which varies in response to changes in temperature of said accelerating electrode.

2. An electron gun as recited in claim 1 wherein the accelerating electrode has an aperture and said temperature sensing means includes a thermocouple disposed as close as possible to said aperture.

3. An electron gun as recited in claim 2 wherein the accelerating electrode is an anode comprised of copper, and the thermocouple comprises a constantan wire welded as close as focusing electrode of an electron beam gun having a cathode and an accelerating electrode which comprises:

sensing the temperature of said accelerating electrode; and

changing the potential applied to said focusing electrode in response to changes in said accelerating electrode tem perature.

5. A method as recited in claim 4 wherein the accelerating electrode is the anode.

6. A method of controlling the potential applied to the focusing electrode of an electron beam gun having a cathode and an accelerating electrode which comprises:

sensing the temperature of said accelerating electrode; and

increasing the potential a plied to said focusing electrode when said accelerating electrode temperature increases until said anode temperature returns to a safe operating level.

7. In combination with an electron beam producing apparatus of the type wherein electrons emitted from a cathode travel through a plurality of apertured electrodes, the improvement which comprises:

means for sensing the temperature of a first apertured electrode; and

means for supplying a negative potential to a second apertured electrode wherein the magnitude of said potential increases when said first electrode temperature increases so that said first electrode temperature decreases.

8. The combination as recited in claim 7 wherein the first apertured electrode is the anode.

9. The combination as recited in claim 8 wherein the second apertured electrode is located between said cathode and said anode. 

1. In combination with an electron gun having an accelerating electrode and a focusing electrode, the improvement comprising: means for sensing the temperature of said accelerating electrode; and means for applying a negative potential to said focusing electrode of said electron gun which varies in response to changes in temperature of said accelerating electrode.
 2. An electron gun as recited in claim 1 wherein the accelerating electrode has an aperture and said temperature sensing means includes a thermocouple disposed as close as possible to said aperture.
 3. An electron gun as recited in claim 2 wherein the accelerating electrode is an anode comprised of copper, and the thermocouple comprises a constantan wire welded as close as possible to said anode aperture.
 4. A method of controlling the potential applied to the focusing electrode of an electron beam gun having a cathode and an accelerating electrode which comprises: sensing the temperature of said accelerating electrode; and changing the potential applied to said focusing electrode in response to changes in said accelerating electrode temperature.
 5. A method as recited in claim 4 wherein the accelerating electrode is the anode.
 6. A method of controlling the potential applied to the focusing electrode of an electron beam gun having a cathode and an accelerating electrode which comprises: sensing the temperature of said accelerating electrode; and increasing the potential applied to said focusing electrode when said accelerating electrode temperature increases until said anode temperature returns to a safe operating level.
 7. In combination with an electron beam producing apparatus of the type wherein electrons emitted from a cathode travel through a plurality of apertured electrodes, the improvement which comprises: means for sensing the temperature of a first apertured electrode; and means for supplying a negative potential to a second apertured electrode wherein the magnitude of said potential increases when said first electrode temperature increases so that said first electrode temperature decreases.
 8. The combination as recited in claim 7 wherein the first apertured electrode is the anode.
 9. The combination as recited in claim 8 wherein the second apertured electrode is located between said cathode and said anode. 